Plants are subject to assault from a variety of diseases that affect growth, flowering, fruiting, and ultimately yield or quality of the plant and plant product. Diseases in plants are caused by sources as diverse as insects, fungi, molds, nematodes, and viruses. Counteractive measures to diseases have been implemented. The use of pesticides, insecticides, fungicides, hormone treatment, and other treatments are widely relied upon. These measures are not always effective or resistance to chemicals develops. Moreover, social acceptance of chemical treatments has waned over the years. Genetic breeding to confer resistance is an environmentally friendly alternative, but labor intensive and difficult to move resistance genes between species of plants. Other mechanisms to confer protection against plant diseases is desirable.
Various genes conferring protection for plants against diseases and insects have been identified. Many of these genes have been cloned as well. Introduction of these genes into plants and control of their expression is important for improving crop development and food production. In addition, transgenic resistance reduces the need for chemicals, which is beneficial for the environment and reduces labor and costs. For effective resistance, expression of the resistance genes in appropriate tissues is critical to their function. As such, tissue-specific promoters and accessory gene products that may increase expression are needed.
One organelle which is particularly important for the expression of genes in higher plant cells is the endoplasmic reticulum (ER). Briefly, the ER comprises the initial site of the protein secretory pathway, the site of the majority of fatty acid modification and triacylglycerol biosynthesis, and the site of an intracellular store of reversibly bound calcium, which is involved in various aspects of plant signal transduction. In developing seed storage tissue, the ER is the primary site of seed storage protein synthesis, folding and assembly. These processes require an array of chaperones, some of which (e.g., BiP, PDI, and GRP94) have been cloned. Calreticulin, which has been cloned as a cDNA from various animals and a few plants (e.g., barley (Chen et al., Plant Cell 6:835, 1994), Arabadopsis (Benedetti and Turner, Plant Physiol. 109:338, 1995), and corn (Napier et al., J. Exp. Bot. 46:1603, 1995)), is the primary calcium binding protein of the ER and may have a role in protein folding, assembly, and signal transduction. Calnexin is another calcium binding, chaperone protein in the ER, which has been cloned as a cDNA from various animals and from Arabidopsis.
The present invention discloses novel compositions for calreticulin and calnexin proteins, genomic sequences, and promoters, use of these proteins and sequences in controlling expression of resistance genes, and further, provides other related advantages.